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Nervous System

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Nervous System The master controlling and communicating system of the body Functions Sensory input monitoring stimuli Integration interpretation of sensory input – PowerPoint PPT presentation

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Title: Nervous System


1
Nervous System
  • The master controlling and communicating system
    of the body
  • Functions
  • Sensory input monitoring stimuli
  • Integration interpretation of sensory input
  • Motor output response to stimuli

2
Nervous System
Figure 11.1
3
Organization of the Nervous System
  • Central nervous system (CNS)
  • Brain and spinal cord
  • Integration and command center
  • Peripheral nervous system (PNS)
  • Paired spinal and cranial nerves
  • Carries messages to and from the spinal cord and
    brain

4
Peripheral Nervous System (PNS) Two Functional
Divisions
  • Sensory (afferent) division
  • Sensory afferent fibers carry impulses from
    skin, skeletal muscles, and joints to the brain
  • Visceral afferent fibers transmit impulses from
    visceral organs to the brain
  • Motor (efferent) division
  • Transmits impulses from the CNS to effector organs

5
Motor Division Two Main Parts
  • Somatic nervous system
  • Conscious control of skeletal muscles
  • Autonomic nervous system (ANS)
  • Regulates smooth muscle, cardiac muscle, and
    glands
  • Divisions sympathetic and parasympathetic

6
Histology of Nerve Tissue
  • The two principal cell types of the nervous
    system are
  • Neurons excitable cells that transmit
    electrical signals
  • Supporting cells cells that surround and wrap
    neurons

7
Supporting Cells Neuroglia
  • The supporting cells (neuroglia or glial cells)
  • Provide a supportive scaffolding for neurons
  • Segregate and insulate neurons
  • Guide young neurons to the proper connections
  • Promote health and growth

8
Astrocytes
  • Most abundant, versatile, and highly branched
    glial cells
  • They cling to neurons and their synaptic endings,
    and cover capillaries

9
Astrocytes
Figure 11.3a
10
Microglia and Ependymal Cells
  • Microglia small, ovoid cells with spiny
    processes
  • Phagocytes that monitor the health of neurons
  • Ependymal cells range in shape from squamous to
    columnar
  • They line the central cavities of the brain and
    spinal column

11
Microglia and Ependymal Cells
Figure 11.3b, c
12
Oligodendrocytes, Schwann Cells, and Satellite
Cells
  • Oligodendrocytes branched cells that wrap CNS
    nerve fibers
  • Schwann cells surround fibers of the PNS
  • Satellite cells surround neuron cell bodies

13
Oligodendrocytes, Schwann Cells, and Satellite
Cells
Figure 11.3d, e
14
Neurons (Nerve Cells)
  • Structural units of the nervous system
  • Composed of a body, axon, and dendrites
  • Long-lived, amitotic, and have a high metabolic
    rate
  • Their plasma membrane function in
  • Electrical signaling
  • Cell-to-cell signaling during development

PLAY
InterActive Physiology Nervous System I,
Anatomy Review, page 4
15
Neurons (Nerve Cells)
Figure 11.4b
16
Nerve Cell Body (Perikaryon or Soma)
  • Contains the nucleus and a nucleolus
  • Is the major biosynthetic center
  • Is the focal point for the outgrowth of neuronal
    processes
  • Has no centrioles (hence its amitotic nature)
  • Has well-developed Nissl bodies (rough ER)
  • Contains an axon hillock cone-shaped area from
    which axons arise

17
Dendrites of Motor Neurons
  • Short, tapering, and diffusely branched processes
  • They are the receptive, or input, regions of the
    neuron

18
Axons Structure
  • Slender processes of uniform diameter arising
    from the hillock
  • Long axons are called nerve fibers
  • Usually there is only one unbranched axon per
    neuron
  • Rare branches, if present, are called axon
    collaterals
  • Axonal terminal branched terminus of an axon

19
Axons Function
  • Generate and transmit action potentials
  • Secrete neurotransmitters from the axonal
    terminals

20
Myelin Sheath
  • It functions to
  • Protect the axon
  • Electrically insulate fibers from one another
  • Increase the speed of nerve impulse transmission
    Formed by Schwann cells in the PNS
  • A Schwann cell
  • Envelopes an axon in a trough
  • Encloses the axon with its plasma membrane
  • Has concentric layers of membrane that make up
    the myelin sheath

21
Myelin Sheath Formation
PLAY
InterActive Physiology Nervous System I,
Anatomy Review, page 10
Figure 11.5ac
22
Nodes of Ranvier (Neurofibral Nodes)
  • Gaps in the myelin sheath between adjacent
    Schwann cells
  • They are the sites where axon collaterals can
    emerge

PLAY
InterActive Physiology Nervous System I,
Anatomy Review, page 11
23
Axons of the CNS
  • Both myelinated and unmyelinated fibers are
    present
  • Myelin sheaths are formed by oligodendrocytes
  • Nodes of Ranvier are widely spaced

24
Regions of the Brain and Spinal Cord
  • White matter dense collections of myelinated
    fibers
  • Gray matter mostly soma and unmyelinated fibers

25
Neuron Classification
  • Structural
  • Multipolar three or more processes
  • Bipolar two processes (axon and dendrite)
  • Unipolar single, short process

26
Neuron Classification
  • Functional
  • Sensory (afferent) transmit impulses toward the
    CNS
  • Motor (efferent) carry impulses away from the
    CNS
  • Interneurons (association neurons) shuttle
    signals through CNS pathways

27
Comparison of Structural Classes of Neurons
Table 11.1.1
28
Neurophysiology
  • Neurons are highly irritable
  • Action potentials, or nerve impulses, are
  • Electrical impulses carried along the length of
    axons
  • Always the same regardless of stimulus
  • The underlying functional feature of the nervous
    system
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